I’ve got an article in today’s New York Times about one of my perennial fascinations—musical hallucinations. One of the reasons that I find this condition so interesting is that it gives us a look under the neurological hood. Our brains do not simply take in objective impressions of the world. They are continually coming up with theories, and they test them against perceptions every moment of our waking lives. It would be impossible to test them against a complete picture of reality, because the world is simply too complex and ever-changing. Instead, the brain makes quick judgments on scraps of information, revising bad theories that don’t make good predictions or using good theories as the basis for actions. Some